Apparatus and method for preventing wear on subsea wellhead assembly or the like

ABSTRACT

Apparatus and method for preventing wear on a subsea wellhead assembly or the like wherein a B.O.P. stack is mounted on the wellhead assembly having a string of pipe extending therethrough down into the well borehole. A plurality of rams are mounted at spaced locations on the B.O.P. stack and movable in a direction generally normal to the central longitudinal axes of the string of pipe. Each ram carries a removable wear pad and all of the rams are movable simultaneously from a first position out of engagement with the string of pipe to a second position where the wear pads abut against and surround the string of pipe. In this manner, any wear of the string of pipe on the B.O.P. stack is taken up by the wear pads which can be removed and replaced when necessary. In addition, drill pipe wiggle is restricted by the engagement of the pipe. Hydraulic fluid may be used to actuate the rams remotely between the first and second positions.

United States Patent [1 1 [111 3,884,298

Watkins May 20, 1975 [541 APPARATUS AND METHOD FOR 3,474.858 10/1969 Gibson et al 175/7 X PREVENTING WEAR O SU SE 3.528.497 9/1970 Lehman 166/.5

WELLHEAD ASSEMBLY OR THE LIKE Primary ExaminerFrank L. Abbott 1 lnvemori Bruce L W3tkin5- P3105 Verdes Assistant Examiner-Richard E. Favreau Estates. Calif.

[73] Assignee: Regan Offshore International, Inc... [57] ABSTRACT Sa Pedro Calif, Apparatus and method for preventing wear on a subsea wellhead assembly or the like wherein a B.O.P. [22] F'led: June 1973 stack is mounted on the wellhead assembly having a [21] A N() 1372,169 string of pipe extending therethrough down into the well borehole. A plurality of rams are mounted at spaced locations on the B.O.P. stack and movable in a [52] US. Cl 166/52, lips/B direction generally normal to the Central longitudinal 1 axes of the ri g of Eac ram carries a rem0v [58] held of Search able wear pad and all of the rams are movable simulta- 166/315 175/5 251/1 neously from a first position out of engagement with the string of pipe to a second position where the wear [56] References cued pads abut against and surround the string of pipe. In UNITED STATES PATENTS this manner, any wear of the string of pipe on the 2.593,?93 4/1952 Rector 251/1 B.O.P. stack is taken up by the wear pads which can 2.721.614 10/ 955 Simmo s 166/77 X be removed and replaced when necessary. In addition, 3,137.348 6/1964 Ah ston fi fi 175/7 X drill pipe wiggle is restricted by the engagement of the 323 2 5 pipe. Hydraulic fluid may be used to actuate the rams 3,299, ei et a 3334606 8/1967 Deal et all u 175/7 X remotely between the first and second positions. 3,459,270 8/1969 Schuh 175/7 7 Claims, 7 Drawing Figures PATENTEU HAYZ 0 I975 SHEET 2 OF 3 PATENTEB HAY 2 0 I975 SHEET 3 BF 3 .w MW mm APPARATUS AND METHOD FOR PREVENTING WEAR ON SUBSEA WELLHEAD ASSEMBLY OR THE LIKE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to subsea wellhead assemblies; and, more particularly, to apparatus and method for preventing wear on B.O.P. stacks associated with the wellhead assemblies.

2. Description of the Prior Art In the oil well industry, blowout preventers (referred to as B.O.P. stacks) are mounted on subsea wellhead assemblies to-hold the pressure within the well borehole associated with the wellhead assembly and ex clude water therefrom. Generally, such assemblies include balljoints thereon which receive therethrough a riser carrying a string of drilling pipe used to carry out the drilling operations. The string of pipe extends through a conventional B.O.P. stack down into the well borehole.

Since the vessel or platform at the surface carrying out these operations moves or floats about with respect to the wellhead assembly, the relatively long string of pipe bends due to differing angles between it and the vessel or platform and, as the string of pipe rotates during drilling operations, may wear a keyway or the like in the lower part of the ball itself or the upper part of the stationary wellhead assembly. When it is necessary to pull out the pipe string, it may get stuck and be extremely difficult, if not impossible, to pull out. Also, wear may occur elsewhere, even on the pipe itself. Such wear weakens the entire drilling operation and is extremely undesirable.

It has been suggested to provide B.O.P. stacks with stationary wear preventing means therein which engage the drill pipe. However, it is necessary in carrying out drilling operations to pass tools or the like through such stacks down into the well borehole. Such stationary wear preventing means restrict the passage of such tools and must be removed before drilling operations can be carried out.

SUMMARY OF THE INVENTION It is an object of this invention to provide apparatus and method for preventing wear on a subsea wellhead assembly when carrying out drilling operations from a vessel or platform at the water surface.

It is another object of this invention to carry out the foregoing object in a manner whereby tools or the like may be run down through the wear preventing apparatus into the well borehole from the water surface.

It is still another object of this invention to carry out the foregoing objects in a remote manner from the water surface.

It is even a further object of this invention to carry out the foregoing objects while restricting movement between the string of pipe and the wellhead assembly.

It is another object of this invention to further provide means for quickly and easily replacing any parts of the wear preventing apparatus that wear out during the drilling operations.

These and other objects are preferably accomplished by providing a B.O.P. stack mounted on a subsea wellhead assembly having a string of pipe extending therethrough down into the well borehole. A plurality of rams are mounted at spaced locations on the B.O.P.

stack and movable in a direction generally normal to the central longitudinal axes of the string of pipe. Each ram carries a removable wear pad and all of the rams are movable simultaneously from a first position out of engagement with the string of pipe to a second position where the wear pads abut against and surround the string of pipe to thereby restrict its movement. In this manner, any wear of the string of pipe on the B.O.P. stack is taken up by the wear pads which can be removed and replaced when necessary. Hydraulic fluid may be used to actuate the rams remotely between the first and second positions.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of apparatus in accordance with the present invention mounted on a wellhead assembly positioned generally above a subsea well;

FIG. 2 is a horizontal view, partly in section, of a portion of the apparatus of FIG. 1 taken along lines Il-II thereof;

FIG. 3 is a view similar to FIG. 2 showing the movement of the rams thereof;

FIG. 4 is a side view, party in section, of one of the ramsof FIGS. 2 and 3, taken along the lines IV-IV thereof;

FIG. 5 is a detailed sectional view of a portion of the apparatus of FIG. 4 taken along lines VV thereof;

FIG. 6 is a detailed sectional view similar to FIG. 4 showing the movement of certain parts thereof; and

FIG. 7 is a horizontal sectional view taken along lines VIIVII of FIG. 4.

DESCRIPTION OF Til-IE PREFERRED EMBODIMENT Referring now to the drawings and more particularly to FIG. 1, a well borehole 10 is shown drilled into the ocean floor l1 beneath the ocean 12, from a floating platform tower, vessel or the like (not shown) located at the surface of the ocean as is well known in the art.

The well borehole 10 has located thereover a conventional wellhead 13 which typically includes a drilling template 14 with an upper cup-shaped shoulder 15. It is to be understood that template 14 normally includes a central bore (not visible in FIG. 1) with lateral passage (also not visible in FIG. 1) extending there-.

through communicating with the ocean 12, which passageways and bore may then be filled with concrete asis well known in the drilling art.

The drilling template 14 has thereover a guide post frame 16 with a downwardly extending cylindrical outer casing 17joined at its upper end with an intermediate portion 18 seating on the shoulder 15 of template 14 as shown. It is to be understood that an inner casing hanger (not visible) is disposed within template 14 for supporting a depending inner casing 19 extending down into borehole 10 for receiving concrete disposed between casing 19 and the well borehole 10 as is also well known in the drilling art.

Intermediate portion 18 is joined to an upper rectangular-shaped portion 20. Upper portion 20 has a plurality of vertically and upwardly extending guide posts 21 with cable anchors 22 on the upper ends thereof for anchoring cables 23 from the surface platform or vessel as is well known in the art.

A conventional Christmas tree unit 24 having a lower guide 25 with a lower tubular protrusion 26 is mounted in fluid communication with casing 19. Unit 24 has a plurality of conventional blow-out preventers 27 mounted thereon under a plurality of spaced upper guides 28. The lowermost blow-out preventor 27 has conventional fluid supply and return lines (not shown) operatively connected thereto as is well known in the art.

As is conventional, unit 24 is lowered from the surface down cables 23 and onto guide posts 21 to be centered by a plurality conically shaped guides 29 carried by guides 25, 28 and uppermost guide arms 30 while the lower tubular protrusion 26 extends into the central bore of the guide post frame 16. The guide arms 30 carry coupling 31 having blow-out preventor fluid control lines (only line 32 being shown) thereon for controlling the opening and closing of the blow-out preventor 27 from the vessel or platform at the ocean surface, all as is well known in the art.

A coupling 33 is provided through the guides 28 to mount the uppermost blow-out preventor 27 to the lower end of a hanger supporting tool 34. It is to be understood that tool 34 may have suitable latching means therein for engaging a casing running tool as is well known in the art.

The upper end of tool 34 is joined to the lower end of a riser 35 leading from the vessel or platform at the surface. Riser 35 may have a bracket 36 extending therearound for mounting fluid lines 37, 38 from coupling 31 to the riser 35 all as is well known in the art.

Extending down the center of riser 35 and the wellhead 13 is a rotatable string of drilling pipe 39 (shown in dotted lines) or the like, the lower end of the lowermost pipe of which is connected to the casing running tool disposed within the hanger supporting tool 34 and which is in turn coupled to well borehole all as is well known in the art.

The riser 35 is shown in FIG. 1 as latched through a conventional marine conductor latch 40 having a ball joint 41 (dotted lines in FIG. 1) therein to allow limited tilting movement of riser 35 as is well known in the art.

A suitable ball joint mechanism which may be used is disclosed in my US. Pat. Ser. No. 3,332,484. The latch 40 is operatively connected to B.O.P. means such as a B.O.P stack 42 which forms the novel aspects of my invention, the structure of which will be described further hereinbelow.

It can be seen from the foregoing that I have described a conventional system for use in subsea operations. The B.O.P. stack 42 will now be described with particular reference to FIGS. 2 through 7.

As particularly contemplated with the present invention, wear preventing means are provided for protecting the apparatus of wellhead 13. In the exemplary embodiment, such wear preventing means comprises a B.O.P. stack 42 as shown in FIG. 2 which includes a housing 43 having a plurality of pressure piston chambers 44 in fluid communication with the inner chamber 45 of housing 43 spaced generally 90 from each other as shown. The total number of placement thereof may of course vary.

Each chamber 44 has associated therewith a ram 46 disposed in each chamber 44. Suitable annular grooves 48 may be provided in housing 43 encircling ram 46 with O-rings 49 therein for assisting in the extension and retraction of rams 46. Each head 50 of each ram 46 has associated therewith a pair of generally arcuateshaped guide arms or jaws 51, 52. A wear bushing or pad 53 is disposed between the jaws 51, 52 and operatively connected to head 50 (see particularly FIG. 3). Each pad 53 is also generally arcuate-shaped on its inner surface 54 as shown. As can be seen in FIG. 2, when rams 46 are extended, the surface 54 abuts against and encircles pipe 39 to restrict movement thereof and prevent wear as discussed hereinabove. Also, as will be explained further hereinbelow, the tip 55 of each jaw overlap and are offset with respect to the tip 55 of an adjacent jaw; for example, the tip 55 of jaw 51 visible in FIG. 2 on the ram 46 on the right overlaps the tip 55 of the jaw 51 of the ram 46 on the left; the tip 55 ofjaw 52 of the ram 46 on the left overlaps the tip 55 of jaw 52 on the right. Of course, the same is true of the remaining jaws 51, 52 not visible in FIG. 2. The jaws 51, 52 are thus located on the heads 50 in such a manner to provide for this overlapping relationship.

It can be seen that, upon the selective application of fluid, such as hydraulic fluid, as will be explained further hereinbelow, from the surface (such connection being provided by any suitable means), the pistons 47 can be selectively extended and retracted to engage pipe 39 (as shown in FIG. 2), then free pipe 39 (FIG. 3) from such engagement. The pads 51, 52 may be removed and replaced when necessary. The selective engagement and disengagement of the pipe 39 permits tools or the like to be run down into well borehole 10 through the stack 42. That is, as shown in FIG. 3, chamber 45 is larger than the inside diameter of riser 35 so that whatever is sent down riser 35 can bypass chamber It can be seen that, in drilling operations, the vessel or platform from which such operations are being carried out at the ocean surface may float about with respect to the riser 35 and the string of pipe 39. At the same time, of course, the wellhead 13 remains stationary. As the pipe 39 rotates, in ordinary drilling operations not using wear preventing means as described hereinabove, the pipe 39 wears a keyway in either the lower part of the ball joint 41 of latch 40 or the upper part of the wellhead 13 as discussed hereinabove.

Thus, the wear preventing means of my invention acts as a saver for preventing wear on pipe 39 or any portion of the wellhead 13. Any wear would occur on pads 53. These pads 53 can be replaced when necessary and retracted to allow for passage of tools, pipe, drill bits, etc. therethrough.

The hydraulic rams 46 permit the pads 53 to close about pipe 39 and restrict the wiggle of pipe 39 and at the same time prevent wear between the pipe 39 and smaller diameter casings hung further down well borehole 10, that is, any concentric casing hung by concentric casing hangers at the wellhead 13 below the B.O.P. stack 42. Since jaws 51, 52 overlap as discussed hereinabove, vertical movement of pipe 39 is prevented when engaging by pads 53.

Again as particularly contemplated within the present invention, ram actuating means are provided for actuating the rams 46. In the exemplary embodiment, such ram actuating means comprises a ram 46, as shown in FIG. 4, having a generally cylindrical outer housing 56 closed off by an end plate 57. Suitable bolts 58 or the like may be used to removably secure plate 57 to housing 56.

Outer housing 56 encloses a generally cylindrical inner housing 59. One or more suitable O-rings 60 may be provided in annular grooves 61 extending about the outer periphery of inner housing 59. Similar, O-rings, such as O-ring 62, may be provided in an annular groove 63 extending about the outer periphery of an inwardly extending reduced portion 64 of end plate 57. As can be seen in FIG. 4, the face of reduced portion 64 abuts against the rear end of inner housing 59 while the rear end of outer housing 56 abuts against the outer periphery of the reduced portion 64 and the face ofend plate 57.

A portion of the outer periphery 65 of inner housing 59 is cutaway to form a passageway 66 between the I outer periphery 66 and the inner cylindrical wall 67 of outer housing 56. As can be seen in FIG. 4, passageway 66 is in fluid communication with passageway 68 extending generally normal thereto formed in outer housing 56. This passageway 68 does not extend all the way through outer housing 56 but is in fluid communication with a passageway 69 formed in the forward end of outer housing 56, which end abuts against the rear face 70 of a generally cylindrical member 71. Member 71 also encircles the forward end of inner housing 59 as shown and has a passageway 72 formed therein axially aligned with the passageway 69 in outer housing 56. Aligned passageways 69, 72 thus extend generally parallel to passageway 61. A passageway 73 is formed through member 71. The opening leading into this latter passageway 73 is closed off by a plug 75, such as a weld or the like. A manifold 149 is formed between plug 75 and passageway 73 and in fluid communication therewith.

As can be seen in FIG. 4, a sleeve member 76, having an axially extending opening 77 therein, is provided between passageways 69 and 72. This may be accomplished by making passageway 69 of a greater diameter than passageway 72 with the opening leading into passageway 72 bevelled, as at bevelled portion 78. The sleeve member 76 includes an enlarged head portion 79 and an integral reduced portion 80. Head portion 79 abuts against the bevelled portion 78 with reduced portion 80 extending into passageway 72. A plurality of suitable O-rings 81 or the like, may be provided in annular grooves 82 extending along sleeve member 76. In this manner, fluid can flow being passageways 72, 73 and 69, through opening 77 in sleeve member 76 without leakage between the joints formed between mem bers 71, 56 and 59. 1

The sleeve member 76' and passageways 69', 72', 73 at the bottom of the cross-section of inner housing 56 and member 71 are similar to member 76 and passageways 69, 72 and 73 respectively. However, instead of passageway 69 communicating with a passageway similar to passageway 68, a passageway 83 is formed within inner housing 56 extending generally parallel to passageway 66 communicating at one end with passageway 69' and at the other end with a passageway 84 extending generally normal thereto and opening at the intersection ofend plate 57, outer housing 56 and inner housing 59 shown. Fluid may flow between these members as will be discussed further hereinbelow.

An annular groove 87 may be provided in the inner peripheral wall 88 of member 71 for receiving O-ring 89 therein.

Aforementioned head 50 is compressed of a wear plate in the form of a ring member 90 encircling the forward end ofinner housing 59. (See particularly FIG. 5). Ring member 90 includes an annularly extending channel 91 formed on its inner surface for receiving therein the end 93 of a pair of oppositely opposed dogs 92 or the like. These dogs 92 abut against the forward end face of inner housing 59 and include elongated keyways 94 on their forward faces 95. These keyways 94 are adapted to receive therein the shanks of bolts 96 (see also FIG. 7).

Each pad 53 includes a tubular portion 97 fitting into a circular cavity 98 formed in a ring-shaped member 99. As can be seen in FIG. 5, the periphery 100 of member 99 fits into the inner peripheral wall 101 of ring member while it abuts against the forward faces of dogs 92. Countersunk apertures 102 may be provided in ring-shaped member 99 for receiving the heads 103 of bolts 96, the shanks of which are threaded through suitable apertures in member 99 and into slots 94. It can be seen that dogs 92, via bolts 96, can slide with respect to member 99 along keyways 94.

The pads 53 may be removably secured to member 99 by providing a plurality of countersunk apertures 104 on the outer surface thereof for receiving bolts 105 therein. The heads 106 abut against the face 107 of member 99 and their shanks 108 are threaded into member 99 as shown (see also FIG. 4).

Referring once again to FIG. 4, each of the guide arms orjaws 51, 52 includes an outer tip or arm portion 109 integral with an offset inner arm portion 110. The end 111 of arm portion is fixedly secured to the outer periphery 112 of ring member 90. A plurality of reinforcing angle plates 113 may be secured to jaws 51, 52 and extend to and abut against inner housing 59 as shown.

A keyway 114 is formed on the outer periphery 65 on both sides of reduced end 115 (see also FIG. 7) and like keyway 114' may be formed in head 50. It can be seen that ring member 90 abuts against the shoulder 116 of end 115. An aperture 117 extends through each side of ring member 90 and a pin 118 is fixedly disposed therein. It should be understood that when the pins 118 enter keyways 114 and 114, this properly aligns wear pads 53 with respect to the axis of the well borehole 10 (i.e., pipe 39).

The end 111 of arm portion 110 includes a depressed portion 119 on its outer periphery. Depressed portion 119 provides a seat for the tip of a dog 120 slidably mounted in an aperture 121 formed in member 71. Dog 120 also includes a slot 122 for receiving the tip 123 of a threaded bolt 124 threaded into an aperture 125 in member 71 extending generally normal to aperture 121. It can be seen that dog 120 is movable with respect to the tip 123 of bolt 125 by means of slot 122.

A passageway 126 extends through member 71 generally normal to aperture 121. A mandrel 127, is disposed in passageway 126 and includes a plurality of 0- rings 128 about its periphery. A passageway 129 of greater diameter than passageway 126 is coaxially aligned therewith. It can be seen that the hex head portion 130 of mandrel 127 abuts against the shoulder of passageway 129 and is threaded therein. It can be understood that release of mandrel 127 permits dog 120 to slide down along slot 122 to release end 111 of arm portion 110.

As can be seen in FIGS. 4 through 6, an axial passageway 132 extends through inner housing 59 communicating at the rear with an aperture 133 in end plate 57 and at the front or forward end with the space 134 between dogs 92. Passageway 132 includes a first portion 135 of a greater diameter than a second portion 136. First portion 135 is internally threaded, as at threads 137, and a mandrel 138 is disposed in passageway 132. Mandrel 138 includes a first threaded portion 139 of greater diameter than a second portion 140. The tip thereof is tapered as at tapered portion 141. A plurality of O-rings 142 are disposed within suitable grooves about the periphery of second portion 140 to prevent fluid leakage therepast from aperture 133. A seat 143 is provided at the entrance of aperture 133 for seating therein a threaded back-off plug 144 having an integral hex nut 145. First portion 139 of mandrel 138 includes a hex opening 148 for receiving an Allen wrench or the like therein so that it can be threaded out of threaded portion 135. In this manner, by removing plug 144 via hex nut 145, mandrel 138 can be unthreaded by means of hex opening 148 and thus backed out of passageway 132.

It can be seen that mandrel 138, by means of tapered portion 141, separates dogs 92 when disposed in space 134 (FIG. When mandrel 138 is backed off after removing plug 144 (FIG. 6), the dogs 92 move inwardly to release ring member 90. End plate 57 may now be unbolted via bolts 58 and the entire inner housing 59, carrying pads 53, can be pulled out and the pads 53 replaced by loosening bolts 105. The pins 118 slide along keyways 114 (FIG. 6) so that no interference is present. The jaws 51, 52 may also be replaced, if desired, as previously described.

As discussed hereinabove, the aforementioned passageway 73 terminates in an annular chamber of manifold 149 closed off by plug 75. A similar plug 75' closes off the bottom passageway 73 and it can be seen that manifold 149 is also in fluid communication therewith (that is, manifold 149 extends about member 71). As indicated by dotted lines 149, suitable communication may be provided between manifold 149 and a source of hydraulic fluid (i.e. lines 150, 151). That is, a single line connection supplies hydraulic fluid to all four rams 46 simultaneously. Thus, suitable hydraulic connections 150, 151 (see FIG. 1) may be provided between stack 42 actuated remotely at the ocean surface for selectively supplying hydraulic fluid under pressure to both sides of annular chamber 149.

Thus, fluid from manifold 149 enters passageways 73', 72', 69, 83 and 84 and flows in the space between the end plate 57 and the rear end of inner houding 59 up into space 133. The O-rings associated with these passageways, sleeve member 76 and members 57 and 59 prevent any fluid from leaking thereout. The fluid thus forces the entire ram assembly forward to permit jaws 51, 52 to engage pipe 39 i.e.., the FIG. 2 position). To make the fluid operate on the ram assembly in the opposite direction, the fluid in the aforementioned passageways is drained off, as by suitable valving means (not shown), to a suitable reservoir or the like (also not shown), and fluid pressure is applied through the other line (e.g., first line 150, then line 151). That is, fluid is directed via manifold 149 through passageways 73, 72, 69, 68 and 66 which forces the entire ram assembly to the FIG. 3 position. The Ofrings associated with these passageways and members 56 and 59 again prevent the fluid from leaking therebetween.

It can be seen from the foregoing that I have described a novel stack saving means wherein rams associated therewith can be actuated to selectively engage a string of pipe or the like. These rams carry wear pads or the like which can be selectively replaced when wear occurs due to the string of pipe bearing against such pads. Further, such positive engagement restricts wiggle of the drill pipe. The foregoing is carried out in a manner whereby the rams may be retracted to permit tools or the like to be passed down into the well borehole.

I claim as my invention:

1. In apparatus for carrying out subsea operations wherein a wellhead assembly is in fluid communication with a well borehole extending down into a subterranean formation, said assembly having a string of pipe extending therethrough from the water surface generally coaxially aligned with said wellhead assembly and down into said well borehole, said apparatus compris- B.O.P. stack means operatively engaging said wellhead assembly and having said string of pipe passing generally coaxially therethrough, said stack means having wear preventing means associated therewith for preventing wear by said string of pipe passing therethrough, said wear preventing means including a plurality of spaced rams selectively movable from a first position in contact with said string of pipe to a second position in a direction generally transverse to the longitudinal axis of said string of pipe, each of said rams having a replaceable wear pad at the forward ends of each of said rams adapted to contact and bear against said string of pipe when said rams are in said first position, said rams being spaced from one another a distance sufficient to pass oil well tools therethrough.

2. A blowout preventer having:

a main stack portion;

a generally central aperture extending through said main stack portion;

a plurality of rams slidably mounted at spaced locations on said main stack portion having replaceable wear pads at the free ends thereof and movable from a first position adjacent the longitudinal axis of said central aperture to a second position away from the axis of said central aperture in a direction generally normal to the longitudinal axis of said central aperture, said rams being spaced from one another a distance sufficient to pass oil well tools therethrough; and

hydraulic fluid means operatively connected to all of said rams for simultaneously moving all of said rams between said first and second positions.

3. Apparatus for prevention wear on a wellhead assembly wherein said wellhead assembly is in fluid communication with a well borehole extending down into a subterranean formation, said assembly having a string of pipe extending therethrough from the water surface generally coaxially aligned with said wellhead assembly and down into said well borehole, said apparatus comprising:

a 8.0.1. stack operatively engaging said wellhead assembly and having said string of pipe passing generally coaxially therethrough, said stack having a plurality of spaced rams thereon movable from a first position engaging said pipe to a second position out of engagement with said pipe, and replaceable wear pads carried at the free ends of said rams which engage said pipe when said rams are in said second position, said rams being spaced from one another a distance sufficient to pass oil well tools therethrough; and

hydraulic fluid means associated with said wellhead assembly operatively engaging all of said rams for simultaneously moving all of said rarns between said first and second positions.v

4. Apparatus for preventing wear on a wellhead assembly wherein said wellhead assembly is in fluid com munication with a well borehole extending down into a subterranean formation, said assembly having a string of pipe extending therethroughfrom the water surface generally coaxially aligned with said wellhead assembly and down into said well borehole, said apparatus comprising:

a B.O.P. stack operatively engaging said wellhead assembly and having said string of pipe passing generally coaxially therethrough, said stack having a plurality of spaced rams thereon movable from a first position engaging said pipe to a second position out of engagement with said pipe, and removable wear pads carried at the free ends of said rams which engage said pipe when said rams are in said second position;

hydraulic fluid means associated with said wellhead assembly operatively engaging all of said rams for simultaneously moving all of said rams between said first and second positions;

a pair of spaced guide arms associated with each of said rams, said guide arms being movable with said rams into an overlapping relationship when said rarns are moved into said first position;

each of said rams including an inner housing carrying said wear pads at one end thereof and an outer housing closing off the end of said rams opposite the ends carrying said wear pads and surrounding all of said rams with said rams being slidably mounted and selectively extendible out of said outer housing, and said hydraulic fluid means includes a first passageway extending between said outer housing in fluid communication with a first chamber formed between each of said rams and the inner wall of said outer housing, said first chamber being disposed between the closed-off end of said rams and the end carrying said wear pads,

a second passageway extending between said outer housing in fluid communication with a second chamber formed between the closed-off end of each of said rams and said outer housing, and the second chamber being sealed-off in a fluid-tight manner from said first chamber, and a manifold in fluid communication with both of said passage ways, and hydraulic fluid inlet means operatively engaging said manifold for selectively supplying hydraulic fluid under pressure to either said first or said second passageways; and

each of said rams includes a flange member disposed at its forward end carrying said guide arms thereon and guide arm guide means associated therewith for guiding said arms into a fixed location'with respect to the longitudinal axis of said pipe, each of said rams further including an axially extending chamber having a mandrel. therein selectively movable from a first position fixedly securing said inner housing to said flange member to a second position releasing said inner housing from said flange memher.

5. The apparatus of claim 4 wherein said outer housing further includes means thereon for releasably locking said flange member thereto.

6. ln apparatus for preventing wear on a wellhead assembly wherein said wellhead assembly is in fluid communication with a well borehole extending down into a subterranean formation, said assembly having a string of pipe extending therethrough from the water surface generally coaxially aligned with said wellhead assembly and down into said well borehole, said apparatus including a B.O.P. stack operatively engaging said wellhead assembly and having said string of pipe passing generally coaxially therethrough, said stack having a plurality of spaced rams thereon movable from a first position engaging said pipe to a second position out of engagement with said pipe, hydraulic fluid means associated with said wellhead assembly operatively engaging all of said rams for simultaneously moving all of said rams between said first and second positions, a pair of spaced guide arms associated with each of said rams, said guide arms being movable with said rams into an overlapping relationship when said rams are moved into said first position, each of said rams includes an inner housing at one end thereof and an outer housing closing off the end of said rams opposite the ends adapted to bear against said pipe and surrounding all of i said rams with said rams being slidably mounted and selectively extendible out of said outer housing, the improvement which comprises:

each of said rams including a flange member disposed at its forward end carrying said guide arms thereon and guide arm guide means associated therewith for guiding said arms into a fixed location with respect to the longitudinal axis of said pipe, and each of said rams further including an axially extending chamber having a mandrel therein selectively movable from a first position fixedly securing said inner housing to said flange member to a second position releasing said inner housing from said flange member. 7. The apparatus of claim 6 wherein said outer housing further includes means thereon for releasably locking said flange member thereto. 

1. In apparatus for carrying out subsea operations wherein a wellhead assembly is in fluid communication with a well borehole extending down into a subterranean formation, said assembly having a string of pipe extending therethrough from the water surface generally coaxially aligned with said wellhead assembly and down into said well borehole, said apparatus comprising: B.O.P. stack means operatively engaging said wellhead assembly and having said string of pipe passing generally coaxially therethrough, said stack means having wear preventing means associated therewith for preventing wear by said string of pipe passing therethrough, said wear preventing means including a plurality of spaced rams selectively movable from a first position in contact with said string of pipe to a second position in a direction generally transverse to the longitudinal axis of said string of pipe, each of said rams having a replaceable wear pad at the forward ends of each of said rams adapted to contact and bear against said string of pipe when said rams are in said first position, said rams being spaced from one another a distance sufficient to pass oil well tools therethrough.
 2. A blowout preventer having: a main stack portion; a generally central aperture extending through said main stack portion; a plurality of rams slidably mounted at spaced locations on said main stack portion having replaceable wear pads at the free ends thereof and movable from a first position adjacent the longitudinal axis of said central aperture to a second position away from the axis of said central aperture in a direction generally normal to the longitudinal axis of said central aperture, said rams being spaced from one another a distance sufficient to pass oil well tools therethrough; and hydraulic fluid means operatively connected to all of said rams for simultaneously moving all of said rams between said first and second positions.
 3. Apparatus for prevention wear on a wellhead assembly wherein said wellhead assembly is in fluid communication with a well borehole extending down into a subterranean formation, said assembly having a string of pipe extending therethrough from the water surface generally coaxially aligned with said wellhead assembly and down into said well borehole, said apparatus compriSing: a B.O.P. stack operatively engaging said wellhead assembly and having said string of pipe passing generally coaxially therethrough, said stack having a plurality of spaced rams thereon movable from a first position engaging said pipe to a second position out of engagement with said pipe, and replaceable wear pads carried at the free ends of said rams which engage said pipe when said rams are in said second position, said rams being spaced from one another a distance sufficient to pass oil well tools therethrough; and hydraulic fluid means associated with said wellhead assembly operatively engaging all of said rams for simultaneously moving all of said rams between said first and second positions.
 4. Apparatus for preventing wear on a wellhead assembly wherein said wellhead assembly is in fluid communication with a well borehole extending down into a subterranean formation, said assembly having a string of pipe extending therethrough from the water surface generally coaxially aligned with said wellhead assembly and down into said well borehole, said apparatus comprising: a B.O.P. stack operatively engaging said wellhead assembly and having said string of pipe passing generally coaxially therethrough, said stack having a plurality of spaced rams thereon movable from a first position engaging said pipe to a second position out of engagement with said pipe, and removable wear pads carried at the free ends of said rams which engage said pipe when said rams are in said second position; hydraulic fluid means associated with said wellhead assembly operatively engaging all of said rams for simultaneously moving all of said rams between said first and second positions; a pair of spaced guide arms associated with each of said rams, said guide arms being movable with said rams into an overlapping relationship when said rams are moved into said first position; each of said rams including an inner housing carrying said wear pads at one end thereof and an outer housing closing off the end of said rams opposite the ends carrying said wear pads and surrounding all of said rams with said rams being slidably mounted and selectively extendible out of said outer housing, and said hydraulic fluid means includes a first passageway extending between said outer housing in fluid communication with a first chamber formed between each of said rams and the inner wall of said outer housing, said first chamber being disposed between the closed-off end of said rams and the end carrying said wear pads, a second passageway extending between said outer housing in fluid communication with a second chamber formed between the closed-off end of each of said rams and said outer housing, and the second chamber being sealed-off in a fluid-tight manner from said first chamber, and a manifold in fluid communication with both of said passage ways, and hydraulic fluid inlet means operatively engaging said manifold for selectively supplying hydraulic fluid under pressure to either said first or said second passageways; and each of said rams includes a flange member disposed at its forward end carrying said guide arms thereon and guide arm guide means associated therewith for guiding said arms into a fixed location with respect to the longitudinal axis of said pipe, each of said rams further including an axially extending chamber having a mandrel therein selectively movable from a first position fixedly securing said inner housing to said flange member to a second position releasing said inner housing from said flange member.
 5. The apparatus of claim 4 wherein said outer housing further includes means thereon for releasably locking said flange member thereto.
 6. In apparatus for preventing wear on a wellhead assembly wherein said wellhead assembly is in fluid communication with a well borehole extending down into a subterranean formation, said assembly having a string of pipe extending therethrough from the water surface generally coaxially aligned with said wellHead assembly and down into said well borehole, said apparatus including a B.O.P. stack operatively engaging said wellhead assembly and having said string of pipe passing generally coaxially therethrough, said stack having a plurality of spaced rams thereon movable from a first position engaging said pipe to a second position out of engagement with said pipe, hydraulic fluid means associated with said wellhead assembly operatively engaging all of said rams for simultaneously moving all of said rams between said first and second positions, a pair of spaced guide arms associated with each of said rams, said guide arms being movable with said rams into an overlapping relationship when said rams are moved into said first position, each of said rams includes an inner housing at one end thereof and an outer housing closing off the end of said rams opposite the ends adapted to bear against said pipe and surrounding all of said rams with said rams being slidably mounted and selectively extendible out of said outer housing, the improvement which comprises: each of said rams including a flange member disposed at its forward end carrying said guide arms thereon and guide arm guide means associated therewith for guiding said arms into a fixed location with respect to the longitudinal axis of said pipe, and each of said rams further including an axially extending chamber having a mandrel therein selectively movable from a first position fixedly securing said inner housing to said flange member to a second position releasing said inner housing from said flange member.
 7. The apparatus of claim 6 wherein said outer housing further includes means thereon for releasably locking said flange member thereto. 